Method and Arrangement Relating to X-Ray Imaging

ABSTRACT

Three-dimensional imaging of a breast tissue is achieved by acquiring a series of X-ray projection images from various angles. A three-dimensional image constructed from the projection images by a computer provides information to the operator to select a coordinate point within the breast from which to obtain a biopsy sample. Acquisition of projection images and construction of three-dimensional images is continued during the insertion of the needle into the breast, during positioning the needle towards the coordinate point, during the sampling and after the sampling. The advantages of utilizing tomosynthesis for breast tissue imaging over stereo imaging include better image quality, easier coordinate measurements within a tissue, ease of use of the equipment by the medical personnel, and fewer image artifact problems.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method and arrangement in X-ray imaging, in particular three-dimensional imaging, and more especially tomosynthesis and biopsy.

BACKGROUND OF THE INVENTION

Tomosynthesis is used to create a three-dimensional image volume of a person's body part, e.g. her breast, or an object, using X-rays. Currently, tomosynthesis breast imaging is available only for research purposes, but an increasing number of market analysts believe it will become more widely used than conventional two-dimensional mammography.

Tomosynthesis is essentially a limited form of Computed Tomography or CT. Normally, several projection images, e.g. 5 or 30, are acquired in a range of different angles, e.g. −10 to +10 degrees. Each projection image is essentially a conventional 2-dimensional digital X-ray image of the examined object. The projection images are then combined using special purpose software for producing a 3-dimensional image volume, which is a 3-dimensional array of voxels, wherein each voxel is essentially a value corresponding to the X-ray attenuation in one point of the real world. The image volume may also be regarded as a stack of layers or slices, wherein each layer or slice is a 2-dimensional image, which can be displayed as normal image. By definition, the layers are oriented essentially orthogonal to the x-ray beams, or in other words such that they are essentially parallel to the projection images. An un-trained viewer may feel that each layer looks like a projection image; despite it is essentially an extraction of structures at a certain depth in the breast. Typically, the thickness of each layer is about 1 to 2 mm, and the pixel size in each layer is 0.05 to 0.2 mm.

Biopsy is a method for extracting tissue from a breast. It is widely used to extract parts of suspected tumors, in particular micro-calcifications. Most commonly, biopsy is performed using stereo-tactic imaging, wherein two 2-dimensional images projection images are acquired from different angle. The operator selects the same target position (most often a microcalc) in both images and a computer determines the three-dimensional coordinates. In most cases, a needle is inserted through a hole in the compression paddle, whereby the breast deformation moves the micro-calcification close to the point of skin penetration. There are also cases where the needle is inserted from directions along the compression paddle, but that implies a longer distance for the needle to travel through the breast.

Speed is important, since biopsy is uncomfortable for the patient, who has her breast compressed and a needle inserted. Most clinics use the same x-ray apparatus for biopsy as for regular mammography examinations, which implies that the patient has to sit on a chair in an upright position during the examination. It happens that patients faint during examination.

SUMMARY OF THE INVENTION

According to the present invention, tomosynthesis has advantages relative to stereo imaging. Tomosynthesis provide better image quality, and future radiologists will be used to tomosynthesis images. Tomosynthesis also avoids trouble when finding corresponding points in two 2-dimensional images, which would otherwise be difficult for clusters of micro-calc or diffuse contours. In the future, many clinics will have only a tomosynthesis apparatus, and that apparatus must be extended to perform biopsy. A typical tomosynthesis apparatus requires less complicated extensions than transforming the apparatus into a stereo apparatus. The reason is that a typical tomosynthesis apparatus is design to obtain many projection images. Each projection image is acquired with a very low dose and thus noisy. Therefore it is not good to pick two projection images and use them for conventional stereo biopsy. The advantage is extra large for multi-slit scanners that are made for acquiring a large number of projection images. Multi-slit scanners are best suitable for tomosynthesis, wherein they perform quick single-exposure acquisition, in contrast to conventional stereo, which requires two separate exposures.

The present invention circumvents the problems about image artifacts, which are caused when the needle is inserted into the image volume.

The needle is inserted in a direction non-parallel (e.g. 45 degrees) to the direction of the x-rays for each projection, and the needle stops a few millimeters before the target position, which contains the tissue to extract. This approach enables image reconstruction without artifacts around the target position.

If the needle points towards the target position, we can be confident that the needle will actually reach the target position if the needle is inserted deeper into the breast, since movements are accurate along the needle direction. Therefore, there is no need to acquire an image when the needle touches the target position.

Preferably, the present invention comprises a patient support 130, a detector unit 150, a needle 210, a compression paddle 140 with a hole for the needle, a needle holder 240, an x-ray source 110, and a computer 230.

In normal operation the workflow is as follows: The breast 170 is compressed between the patient support and the compression paddle 140. A plurality (typically 10-30) of projection images are acquired from the detector unit, during irradiation by the x-ray source. The projection images are views of the breast from slightly different angles. The computer 230 reconstructs a three-dimensional image volume from the projection images, and displays the image volume to the operator. The operator selects what tissue to extract 171, and indicate the position in the displayed image volume. The computer converts the image volume coordinates to coordinates to the needle. A needle actuator inserts the needle into the breast, as in FIG. 1, such that:

-   -   the needle points towards the tissue to extract, and     -   the needle may move close to the tissue to extract, but it shall         reach all the way there, and     -   The needle points in a direction, which is substantially         non-parallel to a plane spanned by the direction of the x-rays         for the different projection images. Preferably, the orientation         is roughly 45 degrees. (The plane can be understood as slice         plane in conventional single-slice CT).

Once again, another set of projection images is acquired, and an image volume is reconstructed. This time, the needle is visible in the projection images, and causes artifacts in the reconstructed image volume. The artifacts propagate along the plane, which is spanned by the direction of the x-rays (more commonly known as slice plane in conventional single-slice CT imaging). Thanks to the clever orientation of position of the needle, there are no image artifacts at the tissue to extract. (The key to understanding the present invention is to understand where artifacts disturb the image volume, and how it depends on the orientation and position of the needle.)

The needle position and orientation is measured, (using the projection images rather than the image volume due to said reconstruction artifacts). The computer estimates the expected path 211 if the needle is inserted deeper into the breast. The computer displays the reconstructed image with overlay graphics showing the needle's position and direction, and displayed. The computer assumes that the needle will be pushed straight inwards and displays the predicted point of intersection with each layer in the reconstructed image volume. FIG. 2 illustrates a user interface for displaying one layer at a time and the predicted path of the needle and the intersection of the viewed layer (red circle).

In case the needle does not point towards the tissue to extract, the needle position is adjusted. The procedure is repeated until images indicate that the needle points towards the tissue to extract.

At this point, the computer knows the distance from the needle to the tissue to extract. The computer shall have information about what kind of needle is connected and where on the needle is the opening for tissue extraction. The needle is inserted an additional distance into the breast, such that the needle opening is at the tissue to extract, and the needle extracts the tissue with a method depending on type of needle.

Some examinations may end by a verification that the desired tissue has been extracted. After tissue extraction, the needle is partially withdrawn, and another image is acquired, wherein the operator can see whether or not the desired tissue has been removed. In case of failure, the needle position may be adjusted in order to obtain more tissue. (This is only possible with needles that can obtain multiple samples, e.g. needle.)

SHORT DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary embodiment of the present invention, wherein the x-ray source (119) is movable in/out relative the figure plane.

FIG. 2 shows an exemplary computer user interface for displaying predicted point of intersection of the needle in each layer.

DESCRIPTION OF THE EMBODIMENTS

The preferred embodiment of the present invention comprises a patient support 130, and a compression paddle 140 for compression of a breast 170 containing a location with some tissue to extract 171. The compression paddle 140 contains a hole for inserting a needle 210 towards said tissue to extract.

Furthermore, the preferred embodiment comprises an acquisition system for obtaining tomosynthesis image data, including a set of projection images (preferably 10-30) and reconstructing a three-dimensional image volume. The acquisition system comprises a detector unit 150, an x-ray source 110, and a computer 230 for reconstruction of a three-dimensional image volume from the set of projection images. The projection images are views of the breast from slightly different angles. The computer 230 reconstructs a three-dimensional image volume from said projection images, and displays the image volume to the operator.

The computer also comprises an algorithm for measuring the needle location and orientation from the projection images. The preferred embodiments avoids measuring the needle position in the image volume, but that requires special care by the image reconstruction algorithm, in order to avoid artifacts, due to dependency of voxel values within a slice, according to well-known prior art of CT image reconstruction.

The preferred algorithm for measurement of the needle position is line fitting to an edge detector, according to prior art. The algorithm may limit the search to an expected region, or perform a full search using the Hough transform or similar.

In the preferred embodiment of the present invention, the computer comprises a user interface for presenting the three-dimensional image volume as a stack of layer images, and there is overlay graphics for presenting the location of the needle, and where it will go if inserted deeper into the breast.

Depending on type of needle and type of examination, the operator may work in different modes. In the first mode, the operator selects a coordinate of the tissue to extract 171, by indicating the position in the displayed image volume. The computer converts the image volume coordinates to coordinates to the needle. In a second mode, the operator does not tell the computer of what to extract. Instead the computer tells the operator the location of the needle, and where it will go if inserted deeper.

The needle will cause image artifacts in the reconstructed image volume. The artifacts spread primarily along the direction of the x-rays and also in the principal plane containing the direction of the set of x-rays through a point.

The preferred embodiment comprises a set of ways for circumventing the problems. Primarily, the needle is inserted substantially non-parallel to said principal plane. The principal plane around the tissue to extract does not contain image artifacts when the needle does not intersect the principal plane containing the tissue to extract.

The preferred embodiment also comprises a function to handle situations when the needle intersect said principal plane. In that case, depending on needle thickness, the image reconstruction either masks the needle prior to reconstruction or of the three-dimensional image volume, or the user interface displays a previously acquired image volume, under assumption that the breast has not moved.

The preferred embodiment comprises a set of these methods depending on needle thickness, location of the opening of the needle (e.g. side or head), amount of tissue to extract, desired accuracy. Some needles are made for hand control, other are suitable for being control by a motor or a hand-driven mechanics. Some needle shall pass the point of tissue to extract. Other extract tissue in the front tip. The preferred embodiment comprises configuration ability for essentially each type of supported needle.

The present invention also comprises a means for constraining the movement of the needle. In particular, the needle shall not penetrate tissue around the ribs of the patient. The preferred embodiment comprises a combination of mechanical stoppers for and software blockers for limiting the amount of needle insertion. The maximum allowed relative movement of a needle is computed using the measurements of the needle position.

The above mentioned and described embodiments are only given as examples and should not be limiting to the present invention. Other solutions, uses, objectives, and functions within the scope of the invention as claimed in the below described patent claims should be apparent for the person skilled in the art. 

1. An apparatus for three-dimensional imaging and extraction of tissue from a human breast, comprising an acquisition means for acquiring a set of projection images of said breast, a reconstruction means for computing a three-dimensional image volume from said projection images, a needle for extracting tissue from said breast, an image analyzer for determining the orientation and location of said needle from said three-dimensional image volume or said projection images, a means for calculating a predicted path of said needle or the movement of said needle in order to reach a target position in said image volume, wherein said projection images are acquired such that directions of the projection through a point in said breast are essentially along a common plane, and the direction of said needle is substantially non-parallel to said plane.
 2. The apparatus according to claim 1, further comprising a computer for computing a predicted path of said needle, wherein said predicted path is the path along which the needle will move if pushed deeper into the breast.
 3. The apparatus according to claim 1, wherein a display is arranged to display an intersection of said predicted path and a layer in said image volume.
 4. The apparatus according to claim 1, further comprising a device for holding and moving said needle, wherein said device comprises a position sensor for determining the position of the needle, along the direction of said needle.
 5. The apparatus according to claim 1, further comprising a guard means for preventing said needle being inserted beyond a boundary.
 6. The apparatus according to claim 1, wherein said target position is a coordinate in said three-dimensional image volume.
 7. The apparatus according to claim 1, further comprising a user interface for selecting said target position.
 8. The apparatus according to claim 1, further comprising a user interface for selecting a layer or slice in said image volume.
 9. The apparatus according to claim 1, further comprising a means for a partial withdrawal of said needle and obtaining a second image for determining whether a target microcalc has been extracted.
 10. The apparatus according to claim 1, comprising a means for displaying the expected point of intersection of said needle in each of said layers.
 11. The apparatus according to claim 1, wherein said acquisition means comprises an X-ray source for emitting X-rays, and said direction of projection is the direction of the X-rays.
 12. The apparatus according to claim 1, further comprising a first and a second multi-slit collimators, and a means for holding either of said first collimator at a first position and said second collimator at a second position during acquisition of said projection images, wherein said second position is further from said breast, whereby the use of said first and second collimators provide different amount of free space around the breast.
 13. An apparatus for three-dimensional imaging and extraction of tissue from a human breast, comprising an acquisition means for obtaining a set of projection images, a needle for extraction of tissue from a location in said breast, a reconstruction means for computing a three-dimensional image volume from said projection images, an image analyzer for determining the location and orientation of said needle from said projection images or data derived thereof, a display means for displaying said image volume together with overlay graphics for showing said location or said orientation or a predicted location, wherein said needle points in a needle direction, and said needle direction is substantially non-parallel to the projection direction through said location in said breast for each of the projection images.
 14. The apparatus according to claim 13, further comprising a needle holder for holding and moving said needle, and a guard for preventing the needle moving beyond a boundary.
 15. The apparatus according to claim 14, wherein movements of said needle can be controlled or constrained from a computer, and said guard is based on a known length of said needle and an angle of said needle.
 16. The apparatus according to claim 14, wherein movements of said needle can be controlled or constrained from a computer, and said guard is based on measured location of said needle.
 17. The apparatus according to claim 13, said needle holder comprising a position sensor or a scale for measurements of a movement along said needle.
 18. A method for extraction of tissue from a body part in an apparatus for tomosynthesis, comprising the steps of holding said body part, acquiring a set of projection images from different angle of said body part, reconstructing a three-dimensional image volume from said projection images, selecting a target position, inserting a needle into said body part close to said target position but not at said target position, acquiring a second set of projection images and reconstructing a second three-dimensional image volume, measuring the needle position and orientation from said second set of projection images or image volume, performing a movement of said needle in direction along said needle for reaching said target position, and extracting said tissue, wherein said method is characterized by inserting said needle in a direction which is substantially non-parallel to the projection direction for each of said projection images.
 19. A computer program comprising instructions for obtaining a set of projection images of a body part, computing a three-dimensional image volume from said projection images, displaying said image volume in a user interface, receiving a target position from said user interface, measuring a the location and orientation of a needle, displaying said location in said image volume, and computing a movement of said needle to reach a coordinate or layer in said image volume, wherein said instructions for measuring uses data from said projection images or data derived thereof, and said needle is non-parallel to a the principal plane containing the direction of projection for each of said projection images. 